Best practice to get a -1V supply from 3.3V/5V?

[0xdeadbeef]

For an OpAmp circuit, I want to create a small negative voltage to be able to reach 0V on the output.
While it's easy to invert e.g. a 3.3V supply with an ICL7660, MAX660 or some discrete charge pump circuit, this will end in e.g. -3.3V, where I just want -1V.
Problem is that most OPs are specified for 6V (Vdd-Vss), so if the positive supply is 5V, the negative supply most not be smaller -1V.
Using an OpAmp with a wider supply range limits the choices quite a bit and in my case would about twice the cost for slightly worse parameters (like offset voltage).
So I would prefer to get something like -0.5 to -1V from the negative supply. I yes, I know about phantom grounds and virtual grounds, but for the moment, I'd rather use a negative supply.

Now I could use e.g. a LM337 to get a voltage closer to-1V, but it's limited -1.25V. Just slightly out of nominal operation condition for e.g. an MCP607x , but still out.
Also e.g. the MAX660 doesn't work for input voltages smaller than 1.5V, so assuming no losses in the inverter, I can't get -1V by using a voltage regulator before the charge pump either.
I guess I could go on further by using a diode or a voltage divider with a voltage follower, but this seems like adding a hell of complexity for something as simply as a low current -1V supply.

So what would be the best practice approach to create -1V from e.g. a 5V supply (while keeping the 6V difference between 5V and -1V)?

[Richard Head]

I'd use a capacitive charge pump with a flying capacitor and clamp the voltage to -1v with a BAV99 or similar. You will need a simple oscillator that can source and sink current. A 555 would work but you may well be able to one of the digital outputs of a micro if you have one available. I'd use an operating frequency of about 10khz.

[bktemp]

Use a LM7705:
www.ti.com/product/lm7705

[Zero999]

Why not use a different op-amp which is rated to more than 6V? Very few op-amps have such a low voltage rating.

http://nonlinear.eecs.berkeley.edu/chaos/LMC6482.pdf
http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/DM00108580.pdf
http://www.st.com/web/en/catalog/sense_power/FM123/SC61/SS1613
http://www.onsemi.com/PowerSolutions/product.do?id=TLV271
http://ww1.microchip.com/downloads/en/DeviceDoc/22243c.pdf

Then there's the MAX44267 which has a built-in capacitive voltage doubler.
http://www.maximintegrated.com/en/products/analog/amplifiers/MAX44267.html

[0xdeadbeef]

Thanks for all the suggestions. Then again, being a lazy sloth, I think I'll try the LM7705.
Sounds like the most elegant solution. One part plus three caps. And the fixed  ?0.232V is just fine.

[Andreas]

Hello,

I would try a LT1054 (regulated voltage inverter).

With best regards

Andreas

[Cliff Matthews]

Won't most cheap maxim negative solutions work with a zener-resistor combo output to get the job done?